Encapsulation ofPsorospermium haeckeli by the haemocytes ofAstacus leptodactylus

Psorospermium haeckeli, a parasite of freshwater crayfish, has sometimes been observed encapsulated within the tissues ofAstacus leptodactylus. This observation does not agree with earlier reports. The lack of tolerance is discussed in relation to variations affecting either the parasite or its host.